1. Field of the Invention
The present invention relates to a liquid discharging head for discharging desired liquid by bubble generation induced by application of thermal energy to liquid, a liquid discharging method, a head cartridge, a liquid discharging apparatus, a liquid discharging printing method, a printing system, a head kit and a head recovery method.
2. Related Background Art
There is already known an ink jet printing method, so-called bubble jet printing method, which achieves image formation by providing ink with energy such as heat to induce a state change in the ink, involving a rapid volume change (generation of a bubble), discharging ink from a discharge opening by the action force based on such state change, and depositing thus discharged ink onto a printing medium. In the printing apparatus utilizing such bubble jet printing method, there are generally provided, as disclosed for example in the U.S. Pat. No. 4,723,129, a discharge port for ink discharge, an ink flow path communicating with the discharge port, and an electrothermal converting member provided in the ink flow path and constituting energy generating means for generating energy for discharging the ink.
Such printing method provides various advantages such as printing an image of high quality at a high speed with a low noise level, and obtaining a printed image of a high resolution, even a color image, with a compact apparatus, since, in the printing head utilizing such printing method, ink discharge ports can be arranged at a high density. For this reason, such bubble jet printing method is being recently utilized not only in various office equipment such as printers, copying machines and facsimile apparatus but also in industrial systems such as textile printing apparatus.
With such spreading of the bubble jet printing technology into the products of varied fields, there have emerged various requirements to be explained in the following.
For example, for a requirement for improving the efficiency of energy, there is conceived optimization of the heat generating member, such as the adjustment of the thickness of the protective film. This technology is effective in improving the efficiency of propagation of the generated heat to the liquid.
Also for obtaining the image of higher quality, there have been proposed a driving condition for satisfactory liquid discharge, realizing a higher ink discharge speed and stable bubble generation, and an improved shape of the liquid flow path for realizing a liquid discharge head with a higher refilling speed of the discharged liquid into the liquid flow path.
Among such liquid flow path shapes, a liquid flow path structure shown in FIGS. 64A and 64B is disclosed for example in the Japanese Patent Laid-open Application No. 63-199972. The liquid flow path structure and the head manufacturing method disclosed in the above mentioned patent application are based on an invention utilizing a backward wave (pressure directed opposite to the discharge opening, namely toward a liquid chamber 12), resulting from the bubble generation.
The invention shown in FIGS. 64A and 64B discloses a valve 10, which is positioned separate from the generation area of the bubble generated by a heat generating element 2 and opposite to the discharge port 11 with respect to the heat generating element 2.
In FIG. 64B, the valve 10 is so disclosed, by a manufacturing method utilizing for example a plate member, as to have an initial position sticking to the ceiling of the liquid flow path 3 and to hang down into the liquid flow path 3 with the generation of a bubble. This invention is disclosed to suppress the energy loss by controlling a part of the above-mentioned backward wave by the valve 10.
However, in such structure, the suppression of a part of the backward wave by the valve 10 is not practical for the liquid discharge, as will be made apparent by the consideration of bubble generation in the liquid flow path 3 containing the liquid to be discharged.
The backward wave itself is not related to the liquid discharge as explained before. At a point when the backward wave is generated in the liquid flow path 3, the pressure resulting from the bubble and relating directly to the liquid discharge renders the liquid dischargeable from the liquid flow path 3 as illustrated in FIG. 64A. It will be apparent, therefore, that the suppression of the backward wave, or a part thereof, does not significantly influence the liquid discharge.
On the other hand, in the bubble jet printing method, a deposit is generated on the surface of the heat generating member by the scorching or cogation of the ink since heating is repeated in a state where the heat generating member is in contact with the ink, and, depending on the kind of the ink, such deposit is generated in a large amount to render the bubble generation unstable, whereby satisfactory ink discharge may become difficult. For this reason there has been desired a method for achieving satisfactory discharge without denaturing the liquid to be discharged, even in case of a liquid which is susceptible to heat or is incapable of sufficient bubble generation.
In view of the foregoing points, a method of constituting the liquid for generating bubble by heat (bubble generating liquid) and the liquid to be discharge (discharge liquid) by different liquids and discharging such discharge liquid by transmitting the pressure of bubble generation to such discharge liquid is disclosed for example in the Japanese Patent Laid-open Application Nos. 61-69467 and 55-81172 and U.S. Pat. No. 4,480,259. In these patents, there is employed a configuration of completely separating the ink or discharge liquid from the bubble generating liquid with a flexible membrane such as of silicone rubber thereby avoiding the direct contact of the two, and transmitting the pressure of bubble generation in the bubble generating liquid to the discharge liquid by the deformation of the flexible membrane. It is intended by such configuration to prevent generation of deposit on the surface of the heat generating member and to improve freedom in the selection of the discharge liquid.
However, in a head of the above-explained configuration where the discharge liquid and the bubble generating liquid are completely separated, the pressure of bubble generation, to be transmitted to the discharge liquid by the elongating deformation of the flexible membrane, is considerably absorbed by such flexible membrane. Also as the amount of deformation of the flexible membrane is not so large, there will result a loss in the energy efficiency and in the discharging force, though the effect of separation of the discharge liquid and the bubble generating liquid can be obtained.
The principal objective of the present invention is to elevate the basic discharge characteristics of the basic method of discharging liquid by generating a bubble (particularly bubble formed by film boiling) in the liquid flow path to a conventionally unexpected level, based on a view point that cannot be anticipated in the past.
A part of the present inventors has made intensive research, based on the basic principle of liquid droplet discharge, to provide a conventionally unavailable liquid discharging method and a head to be used therein. In such research, the analysis of the principle of the mechanism of the movable member in the liquid path has lead to the establishment of a completely novel technology for actively controlling the bubble by positioning the fulcrum and the free end of the movable member in such a manner that the free end is positioned at the side of the discharge port or namely at the downstream side and also by positioning the movable member so as to face to the heat generating member or the bubble generating area, wherein the improvement in the discharge efficiency and the discharge speed is achieved by efficiently directly the growing portion of the bubble at the downstream side thereof toward the liquid discharge direction. Based on these facts, a part of the present inventors has reached an extremely high technical level, in comparison with the conventional one, of actively moving the growing portion of the bubble at the downstream side thereof toward the free end side of the movable member.
The present applicant already filed patent applications on facts that, in the heat generating area for bubble generation, it is preferable to consider the structural components such as the movable member and liquid flow path relating to the growth of bubble in the downstream side, in the liquid flowing direction, of the central line passing through the area center of the electrothermal converting member or in the downstream side of the center of area of the surface governing the bubble generation, and that the liquid refilling speed can be significantly improved by the consideration of position of the movable member and the structure of the liquid supply path. Representative ones of such applications are application Ser. No. 08/586,095, filed Jan. 16, 1996, entitled "LIQUID EJECTING HEAD", application Ser. No. 08/586,260, filed Jan. 16, 1996, entitled "LIQUID EJECTING HEAD", application Ser. No. 08/586,261, filed Jan. 16, 1996, entitled "LIQUID EJECTING HEAD" and application Ser. No. 08/632,667, filed Apr. 15, 1996, entitled "LIQUID EJECTING HEAD".
However, the present inventors have found, in the liquid discharging apparatus in which the discharge liquid and the bubble generating liquid are separated by a movable member, a new drawback that the liquid in a flow path separate from the substrate cannot receive sufficient temperature adjustment by the heater for heating the substrate or by the heater for bubble generation and is also unstable in response time.